I've just rolled my thief and started leveling: Lv18 right now, I think. This isn't going to answer relt's question, since I'm so low as to not be much help for end-game content analysis, but I've been running D/D and Shortbow mostly. I like the Dagger/Pistol combo for the Pistol 5 blind and then stealth using heartseeker (same as Dagger 5, I guess, but the AOE blind for a couple seconds is really helpful.

I also saw a pretty devilish PvP build using Basilisk Venom and 6 runes of Lyssa (the sixth removes all conditions and grants you all boons every time you use your elite skill). It's all about outlasting people until they are at 50% health, and then burst them down using your elite. Interesting for PvP anyway. Look up "Shadow of Lyssa" on youtube.

I also saw a pretty devilish PvP build using Basilisk Venom and 6 runes of Lyssa (the sixth removes all conditions and grants you all boons every time you use your elite skill). It's all about outlasting people until they are at 50% health, and then burst them down using your elite. Interesting for PvP anyway. Look up "Shadow of Lyssa" on youtube.

I've been running a venom build for PvE, looks like I'll have to give it a try in PvP as well. I like boons.

I don't think this is the most recent patch so might not all be relevant, but this was the inspiration for me to try Thief in WvW - I rage so hard at Thieves who pick around and never get a kill, but this guy is good, real good!